I'm going to insert one comment and a related observation about the whole 18.x business:
COMMENT: Anyone who performs a shell login (SSH from elsewhere or <Ctrl><Alt><F1> on the Pi itself) will be greeted by the following:
Welcome to Ubuntu 16.04.5 LTS (GNU/Linux 4.4.38-v7+ armv7l)
* Documentation: https://help.ubuntu.com
* Management: https://landscape.canonical.com
* Support: https://ubuntu.com/advantage
0 packages can be updated.
0 updates are security updates.
New release '18.04.1 LTS' available.
Run 'do-release-upgrade' to upgrade to it.
If you run the software updater in the GUI it will also show up there. So there definitely is an image out there. It downloads, etc. So anyone who hasn't seen this notification has only themselves to blame. But this is where the comment ends...
OBSERVATION: Downloading this image, and running the processor for it only goes so far. It reaches a point where it then says there's not enough room in
/boot. You can make some room by deleting one of two image files (which one depends on the Pi you're using --this is documented BTW), but it's not enough; I think it needs another 4K.
If I read things correctly, the extra space is only needed temporarily (for expansion purposes), so I don't know what the impact would be of moving 4K in overlay files off temporarily. Because I'm a large enough card short, I haven't tried it (if it blows up, I just reformat the card and try again without actual data loss... LOL)
The other thought I had was to mount a blank SD card via USB adapter, and creating a partition table on it (a larger
/boot as FAT32, and the rest as ext4), copying the contents of the system card over, and then swapping cards to try again.
Has anyone managed to do this successfully?